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[yatin <1715660@xxxxxxxxxxxxxxxxxx>]

Closing as bug cleanup, CI issue, and ubunu-xenial not supported since
multiple OpenStack releases

** Changed in: neutron
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/1715660

Title:
  fullstack job failing to create a namespace, hitting kernel deadlock

Status in Linux:
  New
Status in BaGPipe:
  Confirmed
Status in neutron:
  Invalid

Bug description:
  networking-bagpipe fullstack job hits the following kernel issue when
  a new tests are added that use more netns's:

  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel: INFO: "task ip:1358 blocked for more than 120 seconds.
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:       Tainted: G           OE   4.4.0-93-generic #116-Ubuntu
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel: ip              D ffff880166acfdc8     0  1358   1356 0x00000000
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  ffff880166acfdc8 ffff880166acfd98 ffff880205a88000 ffff8800eb29d940
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  ffff880166ad0000 ffffffff81ef78a4 ffff8800eb29d940 00000000ffffffff
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  ffffffff81ef78a8 ffff880166acfde0 ffffffff8183f0d5 ffffffff81ef78a0
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel: Call Trace:
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  [<ffffffff8183f0d5>] schedule+0x35/0x80
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  [<ffffffff8183f37e>] schedule_preempt_disabled+0xe/0x10
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  [<ffffffff81840fb9>] __mutex_lock_slowpath+0xb9/0x130
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  [<ffffffff8184104f>] mutex_lock+0x1f/0x30
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  [<ffffffff8172da4e>] copy_net_ns+0x6e/0x120
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  [<ffffffff810a174b>] create_new_namespaces+0x11b/0x1d0
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  [<ffffffff810a198a>] unshare_nsproxy_namespaces+0x5a/0xb0
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  [<ffffffff81080b41>] SyS_unshare+0x1f1/0x3a0
  Sep 01 14:48:40 ubuntu-xenial-rax-dfw-10739585 kernel:  [<ffffffff818431f2>] entry_SYSCALL_64_fastpath+0x16/0x71

  ( http://logs.openstack.org/66/500066/1/check/gate-networking-bagpipe-
  dsvm-fullstack-ubuntu-xenial-nv/99f751d/logs/syslog.txt.gz )

  (The command that is blocked is an "ip netns add ..." command.)

  This happens in the openstack CI on ubuntu kernel 4.4.0-93-generic.

  On another box (not openstack CI, ubuntu kernel 4.8.0-49), this issue
  seems correlated with a lot of "unregister_netdevice: waiting for lo
  to become free. Usage count = X"  (with varying values for X: 1, 3,
  6).

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